The cyclic shedding of the endometrium is the cause of menses. Prolonged, irregular, or excessive menstrual bleeding, a condition termed menometrorrhagia, has a prevalence of over 20% (Hallberg, L., et al., Acta Obstet. Gynecol. Scand., 45:320-51, 1966). Hysteroscopic endometrial ablation, initially by using laser then popularized by rollerball endometrial ablation, has been in use by gynecologists for over 20 years. Different energy modalities, including hot water, hot water circulating within a balloon, cryotherapy, RF energy, and microwave, have also been used to ablate the endometrium in the treatment of menometrorrhagia. However, all these treatment modalities involve invasive means; that is, all of them require instruments to be inserted through the cervix into the uterine cavity to perform the treatment. In all cases, general, regional, or local anesthesia are required to accomplish the invasive procedure.
Additionally, cervical intraepithelial neoplasia (CIN) and HPV-related lesions on the uterine cervix have a very high prevalence among women, even at an early age. A percentage of the cervical lesions can be related to invasive cervical cancer if left untreated. CIN lesions, especially those involving the endocervical canal, need to be treated to remove all the diseased tissue. Traditionally, cold knife cone biopsy has been used to excise the cervical tissue for treatment. Laser excision and vaporization, cryotherapy, electric cautery and LEEP excision are the other treatment modalities. One concern of these treatment methods is the non-selective destruction of cervix tissue in the general area of the CIN lesions. While the CIN lesions involve only the superficial layer of tissue, the above treatment modalities destroy far more underlying normal cervical tissue than necessary for the purpose of elimination of the lesions. The consequence of excessive tissue damage can lead to cervical incompetence, cervical stenosis, cervical deformities; all can potentially affect future conception rate and pregnancy wastage rate.
More recently, high-intensity focused ultrasound (HIFU) has emerged as a precise, non-surgical, minimally-invasive treatment for benign and malignant tumors. (See, e.g., S. Vaezy, M. Andrew, P. Kaczkowski et al., “Image-guided acoustic therapy,” Annu. Rev. Biomed. Eng. 3, 375-90 (2001)). At focal intensities 4-5 orders of magnitude greater than diagnostic ultrasound (typically about 0.1 W/cm2), HIFU (typically about 1000-10,000 W/cm2) can induce lesions or tissue necrosis at a small location deep in tissue while leaving tissue between the ultrasound source and focus unharmed. Tissue necrosis is a result of focal temperatures typically exceeding 70° C. which can occur with relatively short intervals of HIFU exposure. HIFU is currently being used clinically for the treatment of prostate cancer and benign prostatic hyperplasia, as well as malignant bone tumor and soft tissue sarcoma. Clinical trials for HIFU treatment of breast fibroadenomas and various stage 4 primary and metastatic cancer tumors of the kidney and liver are underway.
Another example of a pathological condition in the female pelvis is a uterine fibroid, which is the most common pelvic tumor in women of reproductive age. Uterine fibroids, or leiomyoma, are benign tumors that cause abnormal uterine bleeding. The incidence of fibroids has been estimated to be 20-25% in women in their reproductive years, although autopsy studies show an incidence upwards of 75%. Approximately ⅓ of these women will have a tumor that is symptomatic requiring treatment.
A major challenge for transvaginal HIFU treatment of uterine pathologies is the deployment of a HIFU therapy transducer having an aperture of adequate size. In general, devices with a larger HIFU aperture tend to optimize the focal length of the HIFU beam and the therapeutic effect of the focused ultrasound energy. However, the size and configuration of the HIFU aperture are generally limited by the size and shape of the vaginal cavity and the location of the cervix and vaginal formices.
Further development of methods and apparatus for providing HIFU therapy in obstetrics and gynecology, as well as other fields of medical endeavor, is desired. In particular, improved methods and apparatus are needed which can provide noninvasive therapeutic treatment of abnormal uterine bleeding conditions and other obstetric and gynecologic pathological conditions. Such treatment includes ablation of the endometrium in the uterus as well as CIN and HPV-related lesions on the cervix.